Hi! Am I allowed to sell templates I make in bootstrap software? On for example themeforest
Yes
Even if I use modules I find in the online section in the software?
The bootstrap framework is open source right - think of this software like photoshop - people sell imagery edited in that so you are good.
The only thing you are tied to that could cause an issue is if you use external sources that have limitations on them such as buying scripts for components that you have to buy a license to use. Otherwise anything within the app is exported as standard code, there are no licenses needed for that. :)